A Practical Solution to Douglas-Fir Seed Orchard Pollen Contamination

Abstract

Based on work by Silen and Keane (1969), research was carried out in the early 1970's to evaluate the effectiveness of delaying reproductive bud development in a Douglas-fir seed orchard by cooling the trees with water spray. The results from these first trials indicated a 10 to 14 day delay in reproductive bud opening giving up to 85% control of local pollen contamination. A solid set irrigation system was then installed for flower bud cooling and was applied to the 1976 and 1978 seed orchard cone crops. In both years phenological and pollen flight data showed results similar to the trials; the operational cooling treatment kept the female reproductive buds unopened through the major portion of the local pollen flight period in approximately 76% of the Douglas-fir clones in the orchard. No adverse side effects have been observed. Calculation of the heat sum and threshold temperatures for Douglas-fir reproductive buds will provide a means to measure the amount of cooling achieved through irrigation and a method to calibrate the irrigation system for most efficient use. The expense of water-cooling as a solution to pollen contamination is justified by the value of the improved seed derived from seed orchard production. The investment is also off-set by the selection of a multi-purpose system that can be applied for irrigation, fertilization and frost protection as well as cooling. Another advantage of the water-cooling is a decrease in the amount of insect infestation in the orchard trees.